Hello!
First of all I want to congratulate you on your buy. The place seems very nice and artistic. I agree that the floors are gorgeous and definitely you have to preserve at least part of them.
About my project:
You suggest to take some of the thickness of the wall but I am not sure how this would affect the floor, so I try to save maximum of the original plan.
I think of few arrangements about the second bath that you want but didn't find a proper solution. So I suggest an additional closet room that you can enclose from the big bedroom. There you can put the washing and dryer machines, as you can add closets for the seasonal clothes and to put hangers and shoe cabinet, because there not enough space in the enter hall.
The big room as you wished is arranged as living room and kitchen. In the corner between the windows I put a little mezzanine as a place for reading or just to be with your thoughts. I really like that kind of corners and I saw that you show pictures with lots of shelves in your references. I suggest a nice armchair and a floor standing lamp. There you can remove the plaster and leave it in bricks. My idea is to put the TV on the railing of the mezzanine. I'm not sure isn't there too high but then you can find some elevating stand. Underneath is the dining room with chairs with addithional lighting. You can see the sofa and the kitchen in the plan.
About the big bedroom I suggest The Bubble chair in the project but any other hanging chair would do the work. I think it would be nice accent. Like in the picture you can divide the wardrobe in three - two for clothes and a part in the middle that can be dressing table or where to put a TV in this room. If the bed is only a platform you can put a wallpaper or to dislodge the bricks again, behind it.
In the junior room there is some low cabinets to put a TV on and wardrobe part. A little desk near the window and the bed with a folding bed under.
I didn't have prices because they vary from the suppliers and the material that you choose to be coverd with. The kitchens and the wardrobes are very specific in prising.